Flex Process - Die Stack

Overview

This process flow has the capability to stack n-High any non modified standard die and semiconductor technology, even with different size. Passive elements such as bypass capacitors can also be embedded in the modules for enhanced signal integrity and electrical performances. It was developed and patented by 3D Plus to enable stack solutions when die are available, and when the highest miniaturization is needed.
This technology is referenced as FLOW 2 and uses the flex layer concept. The die and bypass capacitors are first attached on a layer, so called flex, and connected together and to the flex wings connections. It allows electrical testing and screening of each layer before stacking. This is the key feature for building ‘n’-High stacks with a very good yield. The flex are then stacked vertically and connected thanks to a vertical interconnection technique.
Thanks to its very high reliability and high resistance to harsh environments, this die stacking technology is already used for space applications.

FLOW 2 Die Stack Process Flow Chart

Key Features Benefits
The components are stacked up Small form factor, Size reduction on the PCB, weight savings
Use of bare dice Die scale footprint – Very Low profile stack
The die mounted on flex can be tested and screened before stacking Stacking of n levels with excellent yield
The components are fixed into resin High mechanical resistance, resistance to harsh environments
Humidity resistance enhancement
Used for Space applications
The interconnection is reduced and simplified Higher electrical performance and signal integrity
Simplified PCB layout
The components can be shielded Considerable parasitic effect decrease
Use of well proven technologies Very High reliability
Simplified Manufacturing processes Flexibility and short development time of new designs
Cost effectiveness
Stacks are connection independent Compatibility with all types of components insertion processes : SMT (Gull wing & BGA), Gluing (Conductive column T&B), Through Hole (PGA),…

Flow 2 Die Stack Products Overview

  • Stack of 4 SRAM dice
    with SOP I/Os
  • 4 Stacks of 10 SDRAM dice in a J-lead Ceramic package
  • Stack of 4 RH SRAM
    with SOP I/Os